Manual image scanners are well known devices for inputting textual and pictorial information to a computer. U.S. Pat. No. 4,581,761 describes a typical ergonomically-designed housing including a linear sensor that is manually dragged by the hand of a human operator (hereinafter referred to as the "user") across the text or pictorial copy. A pressure sensitive switch on the bottom of the scanner turns the unit on when the user forces the scanner against the copy, and turns the unit off when the depression force is removed. Additional functions, such as variation of the enlargement or reduction ratio, may be engaged by keys on the top surface of the scanner. Notwithstanding such functionality, the scanner operates in but one scanning mode, that is, it inputs scanned data when the bottom switch is depressed and the linear sensor is swept across the copy. (U.S. Pat. No. 4,901,364 shows another example of a scanner capable of multi-functional operation, but only one scan capability.) If playback of the scan is needed, e.g., to evaluate the pictorial information, either the computer has to collect the linear scan data for a complete raster, or, as shown in U.S. Pat. No. 3,993,865, an intermediate store is provided for first collecting data from the manual scanner at a variable rate dependent on hand motion and then repetitively reading out the data at a constant rate for television viewing.
It is sometimes desirable to formulate a preliminary scan of the copy material before the final scan is obtained. In copending Ser. No. 732,253, entitled "COMPUTER INPUT SCANNER INCORPORATING MULTIPLE SCANNING MODES", which is assigned to the same assignee as the present application, and filed on even date herewith, a scanner useful as an input device for a computer is designed to operate in two scanning modes: a prescanning mode in which subsampled monochrome images are rapidly output to the computer for substantially real-time composition and display, and an input scanning mode in which three successive high resolution color separations are obtained from the composed image. A fixed image is supported on a movable, hand-manipulated stage that interactively controls the conjugate distances of the optical system so that zooming and cropping is obtained without losing focus. By situating the control buttons for the scanning modes on the movable stage, a single hand can control zooming, cropping, and prescanning without having to interact with a keyboard or like input device to the computer.
Apart from the realm of hand-manipulated scanners, relatively larger desk-top scanners are available for high resolution scanning of slides or negatives in color or black-and white. An example is the 35 mm Rapid Film Scanner manufactured and sold by Eastman Kodak Company, Rochester, N.Y. This scanner performs a color sequential high resolution area scan (1312.times.1024 pixel area) of color images in 18 seconds for input to a Macintosh.RTM. computer. Besides performing optical zooming, panning, and cropping, the Rapid Film Scanner has a prescan mode in which the image can be viewed either in monochrome or in color. The user selects the mode via a pull-down menu on the computer. Composing the image in color is difficult, however, because of the slow screen update rate due to the need to sequentially capture three color separations by rotating a filter wheel, and due to the color fringes which appear if the film image is moved while the separations are scanned. As a result, image composition is normally done in the monochrome mode. To then capture the image in color, the user must redirect attention to the computer, pull down the computer menu, and select the color mode. Once the color image is stored in the computer, the white balance may be manually adjusted by using a computer mouse to move screen-based "sliders" which control the gains of the red, green, and blue channels. Unfortunately, this adjustment is time-consuming, and may be difficult for the casual user to master.
A simpler technique for setting proper scene color balance, in particular in a video signal including a luminance component, is described in U.S. Pat. No. 4,679,067. The scene images are developed by scanning a motion picture film and displaying the scanned images. An automatic color corrector electrically balances the three primary colors red, green, and blue relative to luminance in a preselected display area or "window" which is less than the full area of a displayed scene. The window can be moved to any part of the displayed picture and changed in size, so that the corrector concentrates upon a specific portion of the picture having a specific color or monochrome content.
In a scanner operable in multiple scanning modes, such as the 35 Rapid Film Scanner or the aforementioned computer input scanner described in copending Ser. No. 732,253, where the image is first composed in monochrome in a prescan operation before final capture in color, it would be desirable to have the color corrector concentrate upon a selected area. However, the interactive nature of an input scanner, particularly a computer input scanner such as described in copending Ser. No. 732,253, would be compromised by simply electrically balancing the red, green, and blue signals as described in the '067 patent. This happens because the dynamic range is affected by electrical adjustments, and the dynamic range of the picture that was prescanned will be different than the dynamic range of the color balanced picture, that is, what was visible in shadow (or highlight) areas of the prescanned picture may be lost in the color balanced picture.